Assessing COVID IGRA and IgG antibodies in healthcare workers post vaccination.

Introduction: This study evaluated the durability of humoral and cell-mediated immunity (CMI) post Pfizer vaccination among healthcare workers (HCWs) at a tertiary care center in Lebanon.

Methodology: A total of 42 HCWs were enrolled, with their past infection and/or vaccination duration ranging between 2 months and 2 years. Blood samples were tested for COVID CMI and humoral immunity simultaneously. Testing for COVID CMI was done by measuring the interferon gamma-release assay (IGRA) using the QuantiFERON SARS-CoV-2 test, and for COVID humoral immunity using the lateral flow Cellex qSARS-CoV-2 IgG/IgM Rapid Test.

Results: The study group was 69% female and 31% male, aged 22-51 years. SARS-CoV-2 was contracted by 33 (78%) HCWs. Positive COVID humoral IgG and CMI response were found among 35 (83.3%) and 19 (45.2%) HCWs, respectively. Combining the findings for both tests revealed concordant positivity in 35.7%, concordant negativity in 7.1%, Pos IgG - Neg IGRA in 47.6%, and Neg IgG - Pos IGRA in 9.5%.

Conclusions: Generally, no correlation was established between humoral and CMI responses following COVID-19 vaccination. That only 83.3% and 45.2% among the Pfizer-vaccinated HCWs tested positive for COVID humoral and CMI, respectively, prevents substantial conclusions about test reliability for determining immunity status post vaccination. Whether these results are influenced by the specific antigenic epitopes used in the tests or by the potential deterioration of the immune response over time remains to be determined. The incongruity between humoral and CMI responses post-vaccination suggests the need for more comprehensive testing methodologies to assess post-vaccination immunity.